This is the same thing which he had said before, 1 Thessalonians 17:14, which he again repeateth, either to fix it in their memories, that they, calling it to their minds, might direct their lives accordingly, or be thereby fortified against the hatred and malice of the world; for which purpose he told them so before, 1 Thessalonians 15:19, and again in this chapter, 1 Thessalonians 17:14: See Poole on "1 Thessalonians 17:14".
Related Commentaries of John 17:16
John 17:16
16 They are not of the world, even as I am not of the world.